Patent Application
20150102742
This application claims the benefit of Chinese Patent Application No. 201310482881.0, filed on Oct. 15, 2013, which is incorporated herein by reference in its entirety.
The present invention relates to electronics, and more particularly to dimming control circuits, and associated methods.
Silicon-controlled rectifier (SCR) based dimming can be used to achieve voltage regulation or dimming mainly by phase control. For example, the SCR can be turned on in each half cycle of a sine wave, to obtain a same conduction angle. The conduction angle can be changed by regulating operation time or phase of a trigger pulse. For example, an output voltage of a dimmer may be higher and a light can be brighter as the conduction angle is increased.
In one embodiment, a method of controlling dimming can include: (i) generating a dimming signal according to a DC input voltage signal; (ii) generating a voltage average value signal from the dimming signal; (iii) determining whether the dimming signal is in a positive half cycle or a negative half cycle; (iv) comparing the voltage average value signal against an output current feedback signal to generate a first comparison signal, and output a driving signal according to the first comparison signal when the dimming signal is in the positive half cycle; and (v) comparing the voltage average value signal against the output current feedback signal to generate a second comparison signal, and output the driving signal according to the second comparison signal when the dimming signal is in the negative half cycle.
In one embodiment, a dimming control circuit can include: (i) a dimming signal generating circuit configured to generate a dimming signal according to a DC input voltage signal; (ii) a voltage average value signal generating circuit configured to generate a voltage average value signal from the dimming signal; (iii) a half cycle selection circuit configured to determine whether the dimming signal is in a positive half cycle or a negative half cycle, to compare the voltage average value signal against an output current feedback signal to generate a first comparison signal when the dimming signal is in the positive half cycle, and to compare the voltage average value signal against the output current feedback signal to generate a second comparison signal when the dimming signal is in the negative half cycle; and (iv) a driving circuit configured to generate a driving signal according to the first comparison signal when the dimming signal is in the positive half cycle, and to generate the driving signal according to the second comparison signal when the dimming signal is in the negative half cycle.
Reference may now be made in detail to particular embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention may be described in conjunction with the preferred embodiments, it may be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it may be readily apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, processes, components, structures, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention.
Referring now to
In one embodiment, a method of controlling dimming can include: (i) generating a dimming signal according to a DC input voltage signal; (ii) generating a voltage average value signal from the dimming signal; (iii) determining whether the dimming signal is in a positive half cycle or a negative half cycle; (iv) comparing the voltage average value signal against an output current feedback signal to generate a first comparison signal, and output a driving signal according to the first comparison signal when the dimming signal is in the positive half cycle; and (v) comparing the voltage average value signal against the output current feedback signal to generate a second comparison signal, and output the driving signal according to the second comparison signal when the dimming signal is in the negative half cycle.
Referring now to
At 202, a voltage average value signal of the dimming signal can be generated.
For example, a filter circuit can be used to filter the dimming signal, and to generate the voltage average value signal of the dimming signal. In one particular example, the filter circuit can be a low pass filter circuit, such as an RC low pass filter circuit. At 203, it can be determined as to whether the present dimming signal is in a positive half cycle or a negative half cycle. At 204, the voltage average value signal can be compared against an output current feedback signal indicative of a present output current, to generate a first comparison signal or a second comparison signal when the dimming signal is in the respective positive half cycle or the negative half cycle. At 205, a driving signal can be output according to the first comparison signal when the dimming signal is in the positive half cycle, or to the second comparison signal when the dimming signal is in the negative half cycle.
In some cases of SCR-based dimming control, waveforms of the positive half cycle and the negative half cycle may not be uniform in time cycles and amplitude during one or more cycles of the output dimming signal. This can result in differences between dimming signals in the positive half cycle versus the negative half cycle. When output currents in the positive half cycle and the negative half cycle have the same reference signal, potential flicker problems can be substantially avoided. With reference to operation time length of the dimming signal in each half cycle, it can be determined whether the dimming signal is in the positive half cycle or in the negative half cycle. Thus, corresponding dimming control can be realized based on whether the dimming signal is in the positive half cycle or in the negative half cycle.
Thus, a comparison signal for generating a driving signal can be determined according to the dimming signal and the output current feedback signal indicative of the present output current in the positive half cycle or in the negative half cycle in each cycle. For example, an operation time period of the positive half cycle or the negative half cycle in each cycle can be determined. When the dimming signal is in the positive half cycle, the voltage average value signal of the positive half cycle can be compared against the output current feedback signal indicative of the present output current, and an output voltage comparison signal can be provided as a first comparison signal. That is, in the positive half cycle in each cycle, a reference signal for comparing against the output current feedback signal may be the voltage average value signal in the positive half cycle, but not the voltage average value signal in an entire cycle. In this way, flicker that may otherwise be caused by asymmetrical waveforms of the dimming signals in the positive half cycle and the negative half cycle can be substantially avoided.
When the dimming signal is in the negative half cycle, the voltage average value signal of the negative half cycle can be compared against the output current feedback signal indicative of the present output current, and an output voltage comparison signal can be provided as a second comparison signal. That is, in the negative half cycle in each cycle, a reference signal for comparing against the output current feedback signal may be the voltage average value signal in the negative half cycle, but not the voltage average value signal in an entire cycle. In this way, flicker that may otherwise be caused by asymmetrical waveforms of the dimming signals in the positive half cycle and the negative half cycle can be substantially avoided.
For example, the present output current feedback signal can be obtained by way of a current sampling circuit coupled to a main power circuit. When the dimming signal is in the positive half cycle, the driving signal for turning on a switch in the dimming circuit can be generated according to the corresponding first comparison signal in the positive half cycle. When the dimming signal is in the negative half cycle, the driving signal for turning on a switch in the dimming circuit can be generated according to the corresponding second comparison signal in the negative half cycle.
In one embodiment, a dimming control circuit can include: (i) a dimming signal generating circuit configured to generate a dimming signal according to a DC input voltage signal; (ii) a voltage average value signal generating circuit configured to generate a voltage average value signal from the dimming signal; (iii) a half cycle selection circuit configured to determine whether the dimming signal is in a positive half cycle or a negative half cycle, to compare the voltage average value signal against an output current feedback signal to generate a first comparison signal when the dimming signal is in the positive half cycle, and to compare the voltage average value signal against the output current feedback signal to generate a second comparison signal when the dimming signal is in the negative half cycle; and (iv) a driving circuit configured to generate a driving signal according to the first comparison signal when the dimming signal is in the positive half cycle, and to generate the driving signal according to the second comparison signal when the dimming signal is in the negative half cycle.
Referring now to
An input terminal of dimming signal generating circuit 301 can receive a DC input voltage signal obtained via a rectifier circuit, and may generate a dimming signal indicative of a present dimming angle according to a present DC input voltage signal. For example, the dimming signal can represent present dimming information, as may be expected by users. Dimming signal generating circuit 301 can output the dimming signal to voltage average value signal generating circuit 302. Voltage average value signal generating circuit 302 can process the dimming signal, and may generate a voltage average value signal for half cycle selection circuit 303.
Particular embodiments may control dimming using an SCR, and based on half-cycle based control, instead of setting a voltage average value signal of the dimming signal in an entire cycle as a common reference voltage signal to compare with the output current feedback signal in each positive half cycle or negative half cycle. Certain embodiments may be particularly suitable to cases where waveforms of the dimming signal are not uniform in the positive half cycle and the negative half cycle of each cycle, and may substantially avoid related flicker issues.
Referring now to
For example, voltage dividing circuit 401 can include impedance voltage dividing circuit 401 including resistors R1 and R2. Resistor R1 can connect to a positive terminal of rectifier circuit 402, and can connect in series with resistor R2, which can be grounded. Comparator A1 can receive a common node (Vs) of resistors R1 and R2. Resistors R1 and R2 can divide and sample DC input voltage Vg to obtain input voltage sense signal Vs which may be input to comparator A1. Voltage average value signal generating circuit 302 can include RC low pass filter circuit 403. Filter resistor Rf of RC low pass filter circuit 403 can connect between an output terminal of comparator A1 and an input terminal of half cycle selection circuit 303. Filter capacitor Cf can connect to ground and to a common node of filter resistor Rf and an input terminal of half cycle selection circuit 303. RC low pass filter circuit 403 can filter the dimming signal, and may generate the voltage average value signal indicative of the dimming signal voltage average value.
Half cycle selection circuit 303 can include transconductance amplifying circuits Gm1 and Gm2, compensation capacitors C1 and C2, switches S1, S2, S3, and S4, and flip-flop circuit 404. The non-inverting input terminals of transconductance amplifying circuits Gm1 and Gm2 can receive the voltage average value signal, and the inverting input terminals of transconductance amplifying circuits Gm1 and Gm2 can receive the output current feedback signal from current sampling circuit 406.
Switches S1 and S2 can connect in series between an output terminal of transconductance amplifying circuit Gm1, and driving circuit 304. Compensation capacitor C1 may be grounded, and can connect to a common node of switches S1 and S2. Switches S3 and S4 can connect in series between an output terminal of transconductance amplifying circuit Gm2 and driving circuit 304. Compensation capacitor C2 may be grounded, and can connect to a common node of switches S3 and S4.
Clock input terminal CLK of flip-flop circuit 404 can connect to an output terminal of dimming signal generating circuit 301 at comparator A1. Flip-flop input terminal D can connect to the complementary output terminal. Output terminal Q can connect to control terminals of switches S1 and S2. The complementary output terminal of flip-flop circuit 404 can connect to control terminals of switches S3 and S4. Flip-flop circuit 404 can output switching level signals for controlling turn on/off of switches S1, S2, S3, and S4, based on whether the dimming signal is in the positive half cycle or the negative half cycle,
If the dimming signal is in the positive half cycle, switches S1 and S2 can both be on, and switches S3 and S4 may both be off. In this case, the non-inverting input terminal of transconductance amplifying circuit Gm1 can receive the voltage average value signal output by filter circuit 403, and the inverting input terminal can receive an output current feedback signal sampled by current sampling circuit 406. An output terminal of transconductance amplifying circuit Gm1 can provide compensation current it for charging compensation capacitor C1. Compensation voltage signal Vb1 that represents an output current in a positive half cycle may be generated on compensation capacitor C1, and configured as the “first” comparison signal. Also, compensation voltage signal Vb1 may be provided to driving circuit 304.
If the dimming signal is in the negative half cycle, switches S1 and S2 may both be off, and switches S3 and S4 can both be on. In this case, the non-inverting input terminal of transconductance amplifying circuit Gm2 can receive the voltage average value signal output by filter circuit 403. Inverting input terminal of transconductance amplifying circuit Gm2 can receive an output current feedback signal sampled by current sampling circuit 406. An output terminal of transconductance amplifying circuit Gm2 can provide compensation current i2 for charging compensation capacitor C2. Compensation voltage signal Vb2 that represents an output current in a negative half cycle may be generated on compensation capacitor C2, and configured as the “second” comparison signal. Also, compensation voltage signal Vb2 may be provided to driving circuit 304.
For example, current sampling circuit 406 can connect to inductor L of DC-DC converter 407 in the dimming circuit. Current sampling circuit 406 may sample an inductor current, which may be equivalently considered to be a sample of output current io of load (e.g., LED) circuit 408, in order to obtain the output current feedback signal. Also, while DC-DC converter 407 of this particular example is configured in a buck converter topology, any suitable topology (e.g., boost, buck-boost, SEPIC, etc.) can be employed in certain embodiments.
In this particular example, a D-type of flip-flop can be utilized as flip-flop circuit 404. Here, the complementary output terminal of the D flip-flop can connect to flip-flop terminal D, and clock control terminal CLK can connect to an output terminal of comparator A1 to receive the dimming signal. As operation time lengths (e.g., a duty cycle, or active portion of a cycle) of the dimming signal in the positive and negative half cycles may not be uniform, D flip-flop 404 can determine operation time periods of the positive and negative half cycles according to the active (e.g., high level) time duration of the input dimming signal.
When the dimming signal is in the positive half cycle, CLK of flip-flop 404 can receive a high level, and output terminal Q of the D flip-flop can output a high level. Thus, switches S1 and S2 can both be turned on. Also, the complementary output terminal of the D flip-flop can output a low level to turn of switches S3 and S4. When the dimming signal is in the negative half cycle, the dimming signal input to the CLK can be a low level, and output terminal Q of the D flip-flop can also be low. Thus, switches S1 and S2 can both be off, and the complementary output terminal going high can turn on switches S3 and S4. Also, transconductance amplifying circuits Gm1 and Gm2 can each include transconductance amplifiers.
For example, driving circuit 304 can include comparator A2, with the inverting input terminal receiving ramp signal Vramp (e.g., a predetermined ramp signal). The non-inverting input terminal of comparator A2 can connect to switches S2 and S4, in order to receive compensation voltage signal Vb1 output by transconductance amplifying circuit Gm1 in the positive half cycle of the dimming signal, and compensation voltage signal Vb2 output by transconductance amplifying circuit Gm2 in the negative half cycle of the dimming signal.
Thus, when the dimming signal is in the positive half cycle, comparator A2 can receive compensation voltage signal Vb1 for comparison against ramp signal Vramp, and may output the driving signal to control switch Qb in the main power circuit. When the dimming signal is in the negative half cycle, comparator A2 can receive compensation voltage signal Vb2 for comparison against ramp signal Vramp, and may output the driving signal to control switch Qb in the main power circuit. In this way, control of the main power switch can be divided based on positive and negative half cycles of the dimming signal, in order to substantially eliminate flicker in the dimming circuit.
The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201310482881.0 | Oct 2013 | CN | national |
